In the field of aircraft manufacture or assembly, an important consideration is how various assemblies or components are fastened together. Fasteners used in aircraft manufacture or assembly must meet exacting standards for strength, light weight and ease of assembly. An important assembly step in the manufacturing of an aircraft is the fastening or connection of the wing ribs to the wing skin stringers. In the typical wing assembly process, hundreds of fasteners are used. In the prior art, there are two known fastening methods for providing this connection. One approach is to drill holes through the ribs and stringers and bolt the components together using tension bolts. An alternative approach is to use a preformed butterfly clip, sometimes known as a Douglas clip, to fasten the ribs and stringers together.
Generally, a single tension bolt is inserted in complementary holes of the stringer and wing rib and then loaded primarily in tension. The butterfly clip uses a cruciform section that is machined to allow the rib and stringer to be attached to the butterfly clip with four fasteners. Both the tension bolt and the butterfly clip have significant disadvantages.
When a tension bolt is used, the parts or assemblies to be fastened together must have thicker surfaces, where the holes or drilled and the parts come together, to act as bonding pads for the bolts. This adds substantial extra weight to the overall aircraft and requires additional machining of the part. In addition, when the parts are assembled often shims must be added to meet the tight tolerances required in aircraft manufacturing. This adds substantial additional labor costs to the fastening process.
The butterfly or Douglas clips are pre-formed and must be shaped to the individual contours and angles of the assemblies being fastened together. This requires different clips for assembly at different points along the aircraft assembly. There is also a disadvantage in using the butterfly clips as even a one or two degree misalignment between the clip and the part will require shimming which adds to the complexity of the assembly process and increases labor costs. In addition, the actual manufacture of the butterfly clip is expensive since each clip has a complex cruciform shape requiring numerous different shaped parts for a single aircraft. Therefore, a need has arisen for a new method and system for fastening aircraft assemblies that overcomes the disadvantages and deficiencies of the prior art.